The present invention relates to testing of a radio frequency (RF) data packet signal transceiver, and in particular, to testing a packet error rate (PER) of such a device.
Many of today's electronic devices use wireless signal technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless signal technologies must adhere to various wireless signal technology standard specifications.
When designing such wireless devices, engineers take extra care to ensure that such devices will meet or exceed each of their included wireless signal technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless signal technology standard-based specifications.
For testing these devices following their manufacture and assembly, current wireless device test systems typically employ testing subsystems for providing test signals to each device under test (DUT) and analyzing signals received from each DUT. Some subsystems (often referred to as “testers”) include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the DUT, and a vector signal analyzer (VSA) for analyzing signals produced by the DUT. The production of test signals by the VSG and signal analysis performed by the VSA are generally programmable (e.g., through use of an internal programmable controller or an external programmable controller such as a personal computer) so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless signal technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
In such devices, one measure of device receiver performance is packet error rate (PER). The PER is usually expressed as a percentage of the number of packets incorrectly received divided by the total number of packets that were sent and should have been received. When performing non-link testing of wireless devices, where received test data packet signals can be restricted to a single channel, PER testing is not compromised by attempts by the device to find a different wireless access point. However, when performing link testing, the test environment simulates actual operational behavior, including operation by the device where, when the power of the received data packet becomes too low, the device may start to search for a different access point, usually doing so at alternative frequencies or channels.
Hence, during link-based PER testing, where the receive data packet signal power is deliberately made low so as to test worst case performance, it is possible that the DUT may begin searching for a different access point, even as the tester continues to send test data packet signals while counting acknowledgement signals from the DUT (for computation of PER). Accordingly, the tester may interpret, as packet errors, the lack of acknowledgement packets from the DUT during the time that the DUT is searching for another access point, thereby computing a PER test result as being higher than it actually is. This potential problem becomes more significant as the signal power of the test data packets is reduced and approaches the minimum device receiver sensitivity level.
While it may be possible, during link-based PER testing, to prevent the DUT from initiating an access point search, such testing technique would not reflect normal driver operation. Accordingly, this would require modification of the DUT to include special drivers for purposes of PER testing. Therefore, it would be desirable to have a technique by which, from the perspective of the tester, it could be identified when access point searching has begun by the DUT, thereby enabling testing results during this time to be readily identifiable so they can be ignored, thereby allowing correct PER results to be obtained and reflect packet errors only occurring when no access point search is in progress.